title: Suppression of antifolate resistance by targeting the myosin Va trafficking pathway in melanoma.
abstract: Human melanoma is a significant clinical problem. As most melanoma patients relapse with lethal drug-resistant disease, understanding and preventing mechanism(s) of resistance is one of the highest priorities to improve melanoma therapy. Melanosomal sequestration and the cellular exportation of cytotoxic drugs have been proposed to be important melanoma-specific mechanisms that contribute to multidrug resistance in melanoma. Concretely, we found that treatment of melanoma with methotrexate (MTX) altered melanogenesis and accelerated the exportation of melanosomes; however, the cellular and molecular processes by which MTX is trapped into melanosomes and exported out of cells have not been elucidated. In this study, we identified myosin Va (MyoVa) as a possible mediator of these cellular processes. The results demonstrated that melanoma treatment with MTX leads to Akt2-dependent MyoVa phosphorylation, which enhances its ability to interact with melanosomes and accelerates their exportation. To understand the mechanism(s) by which MTX activates Akt2, we examined the effects of this drug on the activity of protein phosphatase 2A, an Akt inhibitor activated by the methylation of its catalytic subunit. Taken together, this study identified a novel trafficking pathway in melanoma that promotes tumor resistance through Akt2/MyoVa activation. Because of these findings, we explored several MTX combination therapies to increase the susceptibility of melanoma to this drug. By avoiding MTX exportation, we observed that the E2F1 apoptotic pathway is functional in melanoma, and its induction activates p73 and apoptosis protease-activating factor 1 following a p53-autonomous proapoptotic signaling event.
authors.affiliation: Department of Biochemistry and Molecular Biology A, School of Biology, Regional Campus of International Excellence "Campus Mare Nostrum", University of Murcia, Murcia, Spain.
authors.forename: María Piedad
authors.initials: MP
authors.lastname: Fernández-Pérez
authors.forename: María F
authors.initials: MF
authors.lastname: Montenegro
authors.forename: Magalí
authors.initials: M
authors.lastname: Sáez-Ayala
authors.forename: Luis
authors.initials: L
authors.lastname: Sánchez-del-Campo
authors.forename: Antonio
authors.initials: A
authors.lastname: Piñero-Madrona
authors.forename: Juan
authors.initials: J
authors.lastname: Cabezas-Herrera
authors.forename: José Neptuno
authors.initials: JN
authors.lastname: Rodríguez-López
mesh_terms: D000818:Animals; D000964:Antimetabolites, Antineoplastic / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects / Q000235:genetics; D045744:Cell Line, Tumor; D004195:Disease Models, Animal; D019008:Drug Resistance, Neoplasm; D050687:E2F1 Transcription Factor / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D005260:Female; D020868:Gene Silencing; D006801:Humans; D008545:Melanoma / Q000235:genetics / Q000378:metabolism*; D008727:Methotrexate / Q000494:pharmacology*; D008745:Methylation / Q000187:drug effects; D051379:Mice; D018995:Myosin Heavy Chains / Q000235:genetics / Q000378:metabolism*; D024701:Myosin Type V / Q000235:genetics / Q000378:metabolism*; D010749:Phosphoprotein Phosphatases / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D000071636:Protein Phosphatase 2C; D021381:Protein Transport / Q000187:drug effects; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects*; D019311:Staurosporine / Q000031:analogs & derivatives / Q000494:pharmacology; D023041:Xenograft Model Antitumor Assays
chemical_list: D000964:Antimetabolites, Antineoplastic; D050687:E2F1 Transcription Factor; C077511:MYO5A protein, human; C054852:7-hydroxystaurosporine; D051057:Proto-Oncogene Proteins c-akt; D010749:Phosphoprotein Phosphatases; D000071636:Protein Phosphatase 2C; D024701:Myosin Type V; D018995:Myosin Heavy Chains; D019311:Staurosporine; D008727:Methotrexate